There used to be a BBC Radio 4 programme brilliantly titled Does He Take Sugar? - the idea behind the name being that anyone who is at all disabled is often treated like an idiot, or worse, by otherwise well-meaning people. It is safe to assume that the cabinet's Thursday tea lady no longer asks Tony Blair about David Blunkett's milk-and-sugar habits, if she ever did. In view of the recent florid publicity about his private life, she may even give him an extra lump, accompanied by a nudge and a wink. As a child he had a budgie called Bimbo.

But, as Stephen Pollard's timely and readable new biography makes agonisingly clear, most of the home secretary's life has consisted on overcoming the disadvantages incurred by virtue of his blindness from birth (modern eye surgery still cannot save such damaged optic nerves) and the social prejudice it provokes. "Come away, let's cross the road, that boy's blind," Blunkett recalls hearing a mother say during his childhood. It was as if he had a contagious disease, he tells Pollard, a New Labour-ish journalist and think-tanker who proves to be an increasingly sympathetic listener.

The result is an unauthorised biography which is none the less avowedly partisan. It gives Blunkett's side of most arguments in his remarkable rise to power, not least his side of the affair with Kimberly Fortier-Quinn and how it was eventually leaked: by a political rival, Blunkett apparently believes. But it is not uncritical. Other voices are heard and Blunkett's faults acknowledged, many of them by the MP for Sheffield Brightside himself, though he is harder on some senior colleagues, from John Prescott down. They resent his candour, while Michael Howard had a field day with this book at Commons question time this week.

What does it tell voters that they did not already know? That Blunkett's saloon bar populism, which offends judges and Guardian readers as well as Prescott, is rooted in the harsh injustices of his impoverished childhood and his persistent refusal to be defeated: he climbs trees, plays football (they fill them with ball bearings to make a noise), even rides a motorbike off road. At his first policy briefing with Blair as education secretary he finds his officials have set the new Braille machine on to the Swedish translation. Never mind. There is a brilliant description of Blunkett, the young Sheffield councillor, listening to constituents' illnesses and problems, knowing he has overcome far worse but cannot say "pull yourself together". Most people are not David Blunkett.

In the long march from youthful Bennery (his was largely a tactical involvement on the lower rungs of power) through Kinnockite modernising to paid-up Blairism, it has helped make him self-reliant, sometimes bad-tempered, even arrogant. His own word is "bumptious." But it also produced sensitivity (an acute sense of mood), a sentimental attachment to all his guide dogs (he rushes to their death beds), and an inner romanticism which drew him to poetry. That was the passion which led him to Mrs Quinn, who was able to accompany him in public for two years without gossip because people fail to grasp (Does He Take Lovers?) that most of his organs work perfectly well. Blindness has its uses in disorientating the sighted. In his current tight corner it may save his career.

Even in Sheffield Blunkett was a third way man, seeking a path between the revolutionary socialism of Militant and Labour paternalism. He canvassed owner- occupied houses because he realised that only canvassing supporters is a recipe for defeat. Pollard reveals the familiar struggle of a progressive politician trying to make theory fit the facts and to reconcile pragmatism with principle. He remains a unilateral disarmer and wary of the EU, but usually keeps quiet about it. It becomes easy to see why he clashes with Gordon Brown, not just a rival for power, but a rival thinker. They are, it transpires, also rivals for the affections of Paul Dacre, Svengali editor of the Daily Mail, one of several media hooligans on whom the home secretary is clearly not planning to serve a well-deserved Asbo. Do Dacre and David read Keats together? One wonders.

As with so much of his career, you couldn't make it up.

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